The present invention relates to the formation of large ring structures. More particularly, it relates to the formation of filament reinforced ring structures having relative large diameters and having a relatively large number of layers of filament reinforcement of the order of 100 to 200 layers or more.
Methods for the formation of filament reinforced structures are disclosed in U.S. patents assigned to the same assignee as the subject application. The preparation of titanium alloy base foils, sheets, and similar articles and of reinforced structures in which silicon carbide fibers are embedded in a titanium base alloy are described in U.S. Pat. Nos. 4,775,547; 4,782,884; 4,786,566; 4,805,294; 4,805,833; and 4,838,337; assigned to the same assignee as the subject application. The texts of these patents are incorporated herein by reference.
Preparation of composites as described in these patents is the subject of intense study inasmuch as the composites have very high strength properties in relation to their weight. One of the properties which is particularly desirable is the high tensile properties imparted to the structures by the high tensile properties of the silicon carbide fibers or filaments. The tensile properties of the structures are related to the rule of mixtures. According to this rule the proportion of the property, such as the tensile property, which is attributed to the filament, as contrasted with the matrix, is determined by the volume percent of the filament present in the structure and by the tensile strength of the filament itself. Similarly, the proportion of the same tensile property which is attributed to the matrix is determined by the volume percent of the matrix present in the structure and the tensile strength of the matrix itself. To achieve high tensile properties in composite structures it is preferred to have a relatively high volume fraction of the filament reinforcement.
Prior to the development of the processes described in the above-referenced patents, such structures were prepared by sandwiching the reinforcing filaments between foils of titanium base alloy and by pressing the stacks of alternate layers of alloy and reinforcing filament until a composite structure was formed. However, that prior art practice was found to be less than satisfactory when attempts were made to form ring structures in which the filament was an internal reinforcement for the entire ring.
The structures taught in the above-referenced patents and the methods by which they are formed greatly improved over the earlier practice of forming sandwiches of matrix and reinforcing filament by compression.
Later it was found that while the structures prepared as described in the above-referenced patents have properties which are a great improvement over earlier structures, the attainment of the potentially very high ultimate tensile strength of these structures did not measure up to the values theoretically possible. The testing of composites formed according to the methods taught in the above patents has demonstrated that although modulus values are generally in good agreement with the rule of mixtures predictions, the ultimate tensile strength is usually much lower than predicted by the underlying properties of the individual ingredients to the composite. A number of applications have been filed which are directed toward overcoming the problem of lower than expected tensile properties and a number of these applications are copending. These include applications Ser. No. 445,203, filed Dec. 4, 1989; Ser. No. 459,894, filed Jan. 2, 1990; and Ser. Nos. 455,041 and 455,048, both filed Dec. 22, 1989. The texts of these applications are incorporated herein by reference.
One of the structures which has been found to be particularly desirable in the use of the technology of these reference patents is an annular article having a metal matrix and having silicon carbide filament reinforcement extending many times around the entire ring. Such ring structures have very high tensile properties relative to their weight particularly when compared to structures made entirely of metal. Such structures must be precise in their internal dimensions in order for the structures to be used most effectively in end use applications inasmuch as the structures are often used as part of a more complex structure and for this purpose are fitted over one or a number of elements in a circular form in order to serve as a reinforcing ring.
One of the structures which is formed has the reinforcing filament wound many times and in many layers around the circumference and is a reinforced ring structure. The reinforced ring can be used for example as a reinforcing ring for the compressor blades of a compressor disk of a jet engine. In order to serve to hold the blades in a compressor stage of a jet engine a large number of layers of reinforcing filaments are required.
The ring structures of concern here are structures which may be a few inches to a few feet in diameter The above referenced prior art patents and pending applications deal primarily with the technology and parameters of forming individual filament reinforced layers and with economical and reliable methods for forming structures having a relatively small number of such layers. However, there is no teaching in the referenced patents and applications about methods for forming ring structures having layers of filament reinforcement in excess of about 100 such layers.
It has been recognized that there is a limitation on the number of layers which can be added to a ring structure before a danger arises that the addition of further layers of filament reinforcement will cause buckling and damage to the filaments of the underlayers. The limit on the number of such layers before the potential for filament buckling and damage occurs is about 20 or 30 layers of filament reinforcement. While such structures are very valuable and are a vast improvement over structures which have been known heretofore, nevertheless there is a need for filament reinforced ring structures having a much larger number of layers of filaments to provide additional reinforcement.
It will be recognized that in forming rings by addition of a single layer of reinforcement at a time, the product ring can be inspected after each layer of reinforcement is added. Rings with a few layers of reinforcement can be discarded if found to be defective when inspected without substantial economic loss. However a single ring to which 60 layers have been added individually does represent a serious economic loss. This is another reason for forming ring segments of 20 layers each and condensing these into a single structure of 100 or 200 layers or more.